The invention is related to the field of slab-coupled optical waveguide lasers (SCOWL), and in particular to a very large mode SCOWL.
High power, single spatial mode diode lasers are important for a number of applications, including pumps for fiber lasers and amplifiers and free space optical communications. The power in a single mode is limited by the size of the single-spatial mode in the diode laser.
The state of the art in large spatial mode diode lasers is the SCOWL. A SCOWL device lasing at a wavelength of 1.0 μm designed with a waveguide thickness of 5 μm has been demonstrated to have a stable single spatial mode with dimensions of 5.7 μm (horizontal direction) by 4.5 μm (vertical direction), where these dimensions are given as full width at 1/e2 intensity. The maximum continuous wave (CW) output power from this device is approximately 2 W.
If one is able to increase the single spatial mode size, then the power should approximately scale with area. This is because the maximum power density at the facet is approximately constant, and is limited by effects such as catastrophic optical damage and thermal roll-over. As the mode area at the facet is increased, the absolute power level at the facet should approximately scale with the mode area.
A simple approach to increasing the mode size that is used with the SCOWL is scaling the waveguide height and ridge width dimensions while maintaining the ratios of T/H and T/W (where T, H, and W are the waveguide height in the slab region, the waveguide height in the ridge region, and the ridge width, respectively) according to the single-mode criteria. However, with this simple approach, one finds that it is extremely difficult to filter out higher order modes, since the higher order modes become more numerous as the waveguide dimensions increase and the propagation constants of the higher order modes also become more closely spaced. In addition, it becomes more difficult to provide sufficient gain to the fundamental mode, while controlling its mode profile. Mode collapse of the fundamental mode (i.e., peaking of the fundamental mode around the active region) can easily occur in such a structure due to strong index guiding in the active region. The core of this invention is the use of additional mode control barrier layers adjacent to the active region to control the vertical profile of the fundamental laser mode and prevent mode collapse.